>Now there's country that traded nuclear weapons for protection by the US that is being invaded by a fascist dictator.
Are you talking about the Budapest Memorandum? According to Wikipedia, it says
>Seek immediate Security Council action to provide assistance to the signatory if they "should become a victim of an act of aggression or an object of a threat of aggression in which nuclear weapons are used".
So AIUI, that's a guarantee that the US will defend Ukraine if Ukraine gets attacked by Russia with nukes. It's not a guarantee that the US will defend Ukraine if Ukraine gets attacked by Russia with non-nukes. So I don't think the US has violated the agreement. Russia violated the agreement by attacking Ukraine (Russia was a signatory, and the treaty also says the parties won't attack each other with any type of weapon).
https://en.wikipedia.org/wiki/Budapest_Memorandum